The present invention relates to a diagnosis system for a valve operating system of an internal combustion engine.
A variety of variable valve operating systems have been proposed. Japanese Patent Provisional Publications No. 7-197846 and No. 8-254126 disclose a variable valve operating system arranged to control a closing timing of intake valves. A Japanese Patent Provisional Publication No. 7-301106 discloses a variable-valve operation-angle control system arranged to variably control an operation angle during a period from opening to closing of intake valves and to control opening and closing timings of exhaust valves. Further, Japanese Patent Provisional Publications No. 7-301105 and No. 7-324609 disclose an electromagnetic type variable valve operating system arranged to properly control opening and closing timings and operation angles of intake and exhaust valves by employing electromagnetic force and springs. Furthermore, a Japanese Patent Provisional Publication No. 6-317117 discloses a diagnosis system which diagnoses a variable valve operating system on the basis of a level of an intake air pulsation of an engine.
However, these conventional variable valve operating systems have been arranged to mainly diagnose the normality thereof by detecting the operating conditions of intake and exhaust valves through further added sensors therefor. Furthermore, the last conventional diagnosis system has been required to be more stable in diagnosis against various changes of the engine.
It is an object of the present invention to provide a diagnosis system for a variable valve operating system of an internal combustion engine, which diagnosis system enables accurate diagnosis of the valve operating systems of intake and exhaust valves without employing another sensors.
A diagnosis system according to the present invention is for a valve system of an internal combustion engine and comprises an airflow meter and a control unit. The airflow meter is disposed in an intake passage of the engine. The airflow meter detects an intake air flow rate of the engine and outputs a signal indicative of the intake air flow rate. The control unit is coupled to the air flow meter. The control unit calculates an accumulated value of an intake airflow rate during a predetermined period and diagnoses the valve system of the engine on the basis of the calculated accumulated value.